Data that is converted between optical and electrical formats when transferred over fiber optics is typically accomplished by using photonic or optoelectronic devices that are contained in modules or subassemblies such as a transceiver module. A transceiver module typically contains a laser transmitter circuit capable of converting electrical signals to optical signals, and an optical receiver capable of converting received optical signals to electrical signals. These modules then interface with host devices such as line cards, routers, networks, host computers, switching hubs, etc., and there are many applications for transceiver modules ranging from fiber to the home, data centers, long haul and high-performance communications.
Transceivers may be manufactured in a form factor called a pluggable, and international industry standard have been adopted to define parameters such as the physical size, shape, and power requirements of these transceivers. Examples include SFP (Small Form-factor Pluggable) transceivers, CFP (C Form-factor Pluggable), XFP (Small Form-factor Pluggable) transceivers, and XFP+ (Enhanced Small Form-factor Pluggable) transceivers. Other transceivers can be built directly onto a circuit card or onto a daughter card that plugs into a main circuit card. With increased data rates, smaller transceiver packages and the need to locate very high capacities of fiber optic input/output on single line cards or low footprint switching boxes, the heat generation due to optical transceivers has become a major problem. Heat generation and power dissipation affect the performance and durability of the transceiver and surrounding components and systems, if the heat is not dissipated from the transceiver to a standard temperature range via air flow or other efficient cooling mechanism for the line card and system that the transceiver is part of. Heat created by heat generating components of the transceiver, such as lasers, modulators, optical amplifiers, receivers and associated electronics and thermal management components, is accordingly removed from devices by passive thermal dissipation or use of an active cooling device. However, the removal of heat using traditional passive dissipation places limits on the technology in the transceiver, particularly the laser transmitter. For high performance systems actively cooled devices increases the complexity and cost of the transceiver as well as the overall power and size.
Further, optical subassemblies and internal devices like Transmitter Optical Subassemblies (TOSA), Receiver Optical Subassemblies (ROSA), photonic integrated circuits and associated driving, detecting, and control circuitry generate heat and may require temperature stabilization to meet the specifications for a certain communications environment and/or application. In addition, certain elements have performance and operating characteristics that are dependent on the device temperature, the ambient temperature range, and the required cooling from the device perspective and the system perspective. There are a variety of techniques to remove the heat from a device or component that is actively cooled, for example forced air cooling, simple convection cooling, or thermoelectric cooling (TEC) and possibly liquid cooling. For high performance transceivers, the amount of heat to be removed requires active cooling which in itself significantly drives up the power consumption and heat dissipation as well as the size of these components. Today, active cooling is typically accomplished using an electrically active device like a thermo-electric cooler (TEC) of the photonic circuits and/or other components that are not designed to be athermal or insensitive to temperature changes. Since many photonic circuits and associated components are not athermal, especially with high performance specifications where data is transmitted and received on the fiber at distances greater than 10 kilometers and where fine optical frequency spacing is employed as in dense wavelength division multiplexing, new energy and costs efficient cooling techniques are needed.
A disadvantage of active cooling, such as with a TEC, is that the TEC itself requires power, generates heat and takes up space. The power consumed can be equal to or greater than that of the components whose temperature is being stabilized. Typical TECs can require up to 3 W or more power depending on the amount of heat that must be transferred from a device to an ambient temperature and the resulting amount of current that must be applied to the TEC to remove the generated heat.
Known prior art attempts to control the temperature of a laser in a communication system include actively cooling the laser with a thermoelectric cooler which is attached to a heat sink. Additional heat is removed from the heat sink using a heat pipe or other solid heat transfer device in a heat transfer relationship between a second heat sink. In other systems, heat pipes are used to cool a laser diode by providing a thermally conductive path between a laser diode heat sink and a thermoelectric cooler heat sink. Examples of such thermal subsystems can be found in U.S. Pat. No. 6,285,476. Disadvantageously, however, these thermal subsystems dissipate heat through a complex system of multiple heat sinks interconnected with heat pipes or solid heat straps which are far removed from the heat generating component of the device, adding to the complexity and size of the device. These systems also employ materials and designs that are not compact enough to form fit into today's optical transceivers or transceiver assemblies or subassemblies, or they employ materials that oxide or corrode limiting the performance lifetime (like copper), or materials that cannot be machine using new micro-channel and nano-feature technologies that satisfy the requirements of heat removal from photonic or optoelectronics devices and/or electronics used in conjunction with these devices.
Therefore, it would be advantageous to develop and implement approaches, methods and apparatus that allow photonic, optical and optoelectronic devices and components to be utilized in real world applications without the use of an active cooling element like a TEC or reduce the amount of work, and therefore the power consumption required to drive the active cooling element under a set of given conditions. It would also be advantageous if the components of the heat removal system are compact to fit into small footprint optical and optoelectronic devices and subassemblies to meet the requirements of today's network devices and have minimal amounts of interconnecting parts for ease of assembly. It would be further advantageous if the device and components can work in the required temperature range for various applications, in particular, the laser and other optics that are housed in the TOSA, and other optics and electronics in the ROSA whose functions are optimized by constant temperature.